Electronic devices are typically used with power conversion circuits. Switched mode power converters are commonly used due to their high efficiency, small size and low weight to power many of today's electronics. Conventional wall sockets provide a high voltage alternating current. In a switched mode power converter a high voltage alternating current (ac) input is converted to provide a well regulated direct current (dc) output. In operation, a switch, included in the switched mode power converter, is utilized to control the desired output by varying the duty ratio (typically the ratio of the on time of the switch to the total switching period) and/or varying the switching frequency (the number of switching events per unit time). More specifically, a switched mode power converter controller may determine the duty ratio and/or switching frequency of the switch in response to a measured input and a measured output.
Conventional power converters include a controller that may be configured to provide a regulated voltage and/or a regulated current at the output of the power converter. In general, a regulated power converter may also be referred to as a power supply. One type of conventional controller monitors a voltage at the output of the power converter in order to provide a regulated output voltage while another type of controller monitors a current at the output in order to provide a regulated output current. A typical way to measure the output current is to include a sense resistor at the output of the power converter such that the output current flows through the sense resistor and the resultant voltage dropped across the sense resistor is proportional to the output current. However, the voltage dropped across the sense resistor is typically large and often referenced to a voltage level different than that of the power converter controller. Hence, additional circuitry, such as an opto-coupler or a bias winding, is often needed to level shift the voltage across the sense resistor in order to interface with the controller.